Exposed resistance electric heater



April 4, 1961 A. w. HAcKMAN 2,978,563 EXPOSED RESISTANCE ELECTRIC HEATER Filed June 12, 1958 2 Sheets-Sheet 2 L25 A n Je 51%? U INVENTOR. 22205 wQO/m c222 United States Patent O lEXPOSED RESISTANCE ELECTRIC HEATER Amos W. Hackman, Kirkland, Ill., assignor to Tuttle Electric Products, Inc., Kirkland, Ill., a corporation of Illinois Filed June 12, 1958, Ser. No. 741,631

6 Claims. (Cl. 219-19) This invention relates to electric heaters of the type in which a helical resistance is mounted in grooves of a body of insulating material to expose the resistance for heating purposes, and has reference more particularly to a. new and improved construction thereof wherein the body of insulating material is a passage defining wall and the resistance is arranged in grooves thereof for exposure to the passage in a distributive manner therearound.

The invention is particularly advantageous -for air heating purposes in appliances, such as clothes dryers, hair dryers, and the like, and provides a simple and compact heating unit which may be manufactured readily at low cost from materials and parts which are readily available, and without elaborate or expensive equipment, It .also provides a unit which is particularly convenient for mounting and readily adaptable to the mounting conditions of the particular installation.

Moreover, in accordance with the present invention, substantial portions of the length of the resistance are completely exposed for free circulation of air therethrough and the heat therefrom is reflected toward and into the passage, both o-f which features contribute materially to the efficiency of the heater.

Furthermore the resistance containing grooves are arranged for positive circulation of air therethrough and through the portions of therresistance therein, and this not only materially increases the heating efficiency but `also avoids overheating of the resistance and excessive heating of the wall in which the resistance is located.

In addition, the construction provides a simple and convenient mounting for the terminals and the location thereof at a place where the resistance is readily attachable thereto, all of which is explained more particularly hereinafter and shown in the accompanying drawings, in which:

Fig. 1 is an end view, with certain portions in section, of a heater made in accordance with the invention;

Fig. 2 is a sectional view of the heater of Fig. 1 taken along the line 2-2 thereof;

Fig. 3 is a perspective view of a mold which may be utilized for making the heater of Fig. 1;

Fig. 4 is a side view showing facilities for mounting the heater in the opening of a wall;

Fig. 5 is an end view of a modified form of heater;

Fig. 6 is a longitudinal sectional view of the heater of Fig. 5 taken on the line 6 6 thereof;

Fig. 7 is a fragmentary view of the open side of a resistance containing groove having facilities at intervals therealong for holding the resistance therein;

Fig. 8 is an enlarged sectional view on the line 8-8 of Fig. 8; and

Fig. 9 shows an end view of a modification of the heater to provide dual passage circulation.

Referring now to the drawings and particularly to Figs. 1 and 2 thereof, the heater thereof comprises a body 11 of heat resistant electrical insulating material, such `as a ceramic, formed in the shape of a hollow cyl- ICC inder with relatively thick annular wall 12 defining a passage 13 which is open at the opposite ends. Preferably this wall is confined in and supported by a cylindrical shell 14 with the ends of the shell extending beyond the ends of the cylindrical body 11 as indicated at 15 in Fig. 1.

The inner face of the wall 12 is provided with a plurality of equally spaced, axially extending grooves 16 which are open at their opposite ends and adapted to contain and support portions of an elongated and continuous resistance heating element which is indicated as a whole by the reference numeral 17. This resistance 17 is of conventional helical coil type, as shown, and is wound back and forth through-the grooves 16 and has loops or return bend portions 18 which extend openly beyond the opposite ends of the wall 12 so that air may circulate freely therethrough. The grooves 16 have lip portions 19 at opposite sides along their entrances extending toward one another suiciently to retain the resistance in the grooves and when thus constructed the resistance is necessarily installed by threading it endwisve through successive grooves.

Terminals 20 are provided to which the opposite ends of the resistance are connected for rsupply of current thereto and in the construction of Figs. l and 2 these terminals are mounted on one projecting end 15 of the shell 14 and the grooves 16 are of such number and arranged so that the opposite ends of the resistance 17 lead out ofthe corresponding ends of two adjoining grooves 16 at places substantially coinciding with the positions of the respective terminals 20.

These terminals 20 are of a conventional nature in the form of stems which are headed at their inner ends as at 21 and threaded at their outer ends to accommodate nuts 22 and between the nuts 22 and the heads 21, extend through porcelain insulators comprising inner and outer parts 23 and 24 respectively by which the stems 20 are safely insulated from the shell 14. The resistance has the wire thereof at opposite ends bent around the respective stem 20 and clamped between the head 21 and inner insulator port 23 of the stem.

This heater, as above described, is usable particularly to heat air circulated through the passage 13 by a blower and the return bends 18, being in the open permit free circulation of air therethrough for efficient dissipation of heat thereto and moreover, as the opposite ends of the grooves 16 are open and the resistance of open coil form, air is circulated through the grooves and through the portions of the resistance therein to extract heat therefrom and cool the portions of the wall 12 at the grooves and avoid possible overheating of those portions of the `resistance which might otherwise occur on account of the extent of confinement thereof.

Fig. 3 illustrates a mold that may be used to form the cylindrical body illustrated in Figs. l and 2. In Fig. 3 a disc-like mold base 25 supports an upstanding cylindrical core 26 concentrically on the base 25 and this core has a plurality of longitudinally extending ribs 27 therearound which are suitably spaced apart and of a cross sectional shape which is the counterpart of that of the grooves 16 and serves to form said grooves in the molding process.

A shell 28 is frictionally applicable to the periphery of the base 25 to be held thereby in an upright position concentric with the core 26 to form between the latter and the shell a mold cavity in which the wall 12 is formed, and this shell may be a part of the mold equipment or it may be the shell 14 of the heater and retained on the wall 12 after the latter is completed.

When the shell 28 thus'used in the molding is retained on the wall 12 to constitute the shell 14 of the heater, the base 25 is preferably of such depth to accommodate agresse .a sutiicient portion of the length of the shell 28 thereon to provide the end extension which is shown at the upper end of the heater of Fig. 2 and at its upper end the shell 28 is provided with openings, as indicated at 29 in Fig. 3., to provide the openings in the shell 14 for securement of the terminals thereto.

After the shell 28 is assembled with the base 25 and core 26, as aforesaid, the annular space betweenthe core 26 and the shell 28 is filled with a plastic mass of harden- -able material, such for example, as steatite, up to the level to provide the required length of the wall l2 and after it is sufficiently hardened the base and core 26 `are removed from the molded mass and the shell 23 also `unless itis to`be retained thereon to provide the wall 14,

and after the molded material is suliiciently hardened, by baking or otherwise, the resistance i7 is threaded through the grooves i6, the terminals 2@ applied to the shell i4 and the ends of the resistance connected to the terminals 2i) and the heater is ready for use.

Instead of utilizing the shell 14 as the shell 28 of the mold, a shell 28 may be provided for molding purposes only and the shell 14 may be applied on the wall i2 after the latter is molded.

Heaters of the character described above are usable in clothes dryers and usually placed in an appropriate opening of a wall or partition ofthe dryer so that air supplied by a blower, at one side of the wall or partition, is forced through the passage i3 of the heater to the other side of the wall or partition of the dryer, and in Fig. 4 the reference numeral Btl indicates a portion of such wall or partition having an opening 3l. to accommodate the heater which is indicated in said figure at32.

This heater 32 may be provided with the shell 14, as shown in Figs. l and 2, or with the shell 14 omitted, and for mounting in the opening 3i. has a strap 33 clamped therearonnd and this strap has an outwardly extending flange 34 with bolt holes corresponding to bolt holes around the opening of the partition to receive bolts 35 for securing the heater 52 in or at the opening 31.

This provides a particularly inexpensive and convenient mounting of the heater 32 and the heater may be adjusted to project to any extent through the opening 31 or may be located entirely at one side of the partition 3i).

The embodiment of the invention of Figs. 5 and 6 is similar to that of Figs. l and 2. in the respect that it comprises a cylindrical or substantially cylindrical body 36 of ceramic material with a passage 37 therethrough and the annular wall of the body 36 is provided in the inner as indicated at 41 and 42 to accommodate the return bend portions 4t) Within surrounding end portions 43 and 44 of the body or wall 36 which project beyond the return bends 40.

At one end of the body 36 the wall thereof is externally shouldered at 'to increased thickness at that end where the counterbore 42 and end portion 44 are located and this thickenedcounterbored portion 44 isprovided with a pair of circumferentially spaced relatively deep notches 46 to receive therein terminals 47 to the inner ends of which the ends of the resistance 39 are connected. respectively. Thus the terminals 47 are readily applicable side- Wise in the notches and they are secured therein by clamping the interposed portion of the thickened end portion 44 of the body wall between an enlargement 48 ofthe terminal and a nut 49 thereon, the said portion 44 `being preferably provided at these places with internal .4, and external flat faces 50 to facilitate said clamping engagement.

As above mentioned, these heaters are particularly advantageous for use in connection with blowers which are arranged to circulate a large volume of air through the heater passage, such blower being indicated at 51 in Figs. 4 and 6 with a connection, which is indicated diagrammatically at 52 in Fig. 4 and at 53 in Fig. 6, whereby the air supplied from the blower is conducted to one end of the respective heater of Figs. 4 and 6 so that it is required to flow through the passage of the respective heater, the connection 52 being representative of a compartment at one side of the partition 30 to which the air is supplied by the blower as is common practice in clothes dryers and the llike and the connection 53 being representative of a connection leading directly to one end of the heater as is customary in hair dryers and the like, and it will be understood Vthat the air thus supplied is required to pass through the passage of the heater wherein it is exposed to heat from the portions of the resistance in the grooves and also passes in intimate contact with the exposed return bends 40 `and through the grooves from end to end thereof in intimatecontact with the portions of the resistance therein.

Heat is radiated into the passage and reflected thereinto by the walls 12 and 36, and as the shell ends 15 of Figs. l and 2 and wall extensions 43 and 44 of Fig. 6 extend around the return bend portions of the resistances, these shell ends 15 and extensions reilect the heat from the exposed resistance return bends into Ithe path of air blowing through the passage.

TheV grooves 16 and 38, instead'of being of the form shown in Figs. 1 and 2 with lips 19 throughout the length of the grooves for holding the resistance therein, may be of full width at their entrance with overhanging ears 54 as shown in Figs. 7 and 8 longitudinally spaced at opposite sides of the groove to hold the resistance therein and by reason of the longitudinal spacing of the ears the resistance portions to be located in the grooves may be laid sidewise in the grooves instead of inserted endwise.

The ceramic annular wall of the heater may be provided with longitudinal grooves in the inner face and provided with resistance as explained hereinbefore and in addition may also be provided in the exterior face with similar grooves and resistance and with a surrounding wall spaced therefrom to provide a heated air passage through the heater body as in Figs. 1 and 2 and 5 and 6 and iny addition to provide a heated annular air'passage aroundthe heater body as shown in Fig. `9.

Thus in said Fig. 9 the reference numeral 55 is the annular ceramic wall with passage 56 therethrough and provided in the inner face with grooves 57 having the resistance 58 thereinas in Figs. l and 2 and 5 and 6 and in this respect the `ceramic body and grooves and resistance arrangement is the same as in either Figs. l and 2 and Figs. 5 and 6.

n l The ceramic wall in Fig. 9, however, is lprovided 1n addition with a series of longitudinally extending circumferentially spaced grooves 59 in the outer face thereof with resistance 60 extending back and forth therethrough with exposed return bend portions 61 at opposite ends of the, grooves. and this heater is contained in a surrounding shell 62 which is spaced therefrom to provide an annular passage 63 which is heated by the exmetal shell which is open at its opposite ends, a mass of electrical insulating material solidified against the inner face of the shell in molded conformity thereto and providing a thick rigid tubular wall extending around and defininga passage which is open at its opposite ends, said wall having at each end of the passage an exposed outwardly presented end face beyond which one of the opposite ends of the tubular shell projects, said wall being provided in the passage defining face thereof with a plurality of passage facing grooves laterally spaced at intervals around the passage and extending lengthwise of the passage from end to end thereof and through said outwardly presenting end faces of the wall, a long helical coil of resistance wire mounted in the grooves and extending from end to end thereof and provided with return bend portions of the coil each composed of a plurali-ty of convolutions of the coil projecting beyond the end faces of the said tubular wall and connecting the portions of the coil within the grooves to one another, the said grooves having inturned portions at the mouth thereof by which the coil is retained in the grooves and the shell having end portions thereof projecting beyond the wall and the said return bend portions and providing an enclosure for said return bend portions, and a pair of terminal members which project outwardly through the shell at at least one of said extended end portions thereof and are electrically insulated from one another and have the opposite ends of the resistance Wire of said coil connected respectively thereto.

2. An air heater of the class described comprising a long helical coil of electrical resistance wire, a rigid onepiece tubular body by which the helical coil is supported, and a blower by which air circulation is enforced in a path leading through the tubular body, said body comprising a mass of electrical insulating material forming a thick wall surrounding and dening a passage around which the helical coil is distributively disposed, the passage being open and unobstructed at its opposite ends providing free entrance of the blower circulated air to the passage at one end thereof and free exit of the blower circulated air from the passage at the other end thereof, said wall having an exposed outwardly presented end face around each open end of the passage and said wall being provided in the passage defining face thereof with a plurality of passage facing grooves laterally spaced at intervals around the passage and extending lengthwise of the passage from end to end thereof and through said outwardly presented end faces of the wall and providing the groove with open opposite ends for entrance and exit of the blower circulated air through the grooves from end to end thereof, the helical coil being extended back and forth through the grooves with portions thereof contained in the grooves and exposed to the passage and other portions thereof projecting outwardly from the groove ends beyond said end faces of the wall at the entrance and exit ends of the passage and providing exposed return bends which connect the portions of Vthe helical coil in the grooves with one another, the said other end portions which project outwardly and provide the exposed return bends at the entrance end of the passage having the successive convolutions of the resistance wire thereof spaced apart and providing entrance of blower circulated air therebetween into the interior of the portions of the helical coil within the grooves and the spaced apart convolutions at the exit end of the passage providing exit therebetween of blower circulated air from the interior of the helical coil portions within the grooves, the said Wall having portions along the grooves which obstruct lateral displacement of the helical coil portions from the grooves toward the passage and retain said helical coil portions in the grooves.

3. An air heater as defined in claim 2 in which a tubular skirt portion projects from the thick wall beyond each end face thereof and provides an enclosure around said return bends.

4. An air heater as defined in claim 2 in which the tubular body has a counterbore beyond each end face of the thick wall providing said thick wall with a tubular thin wall extension projecting beyond each end face and enclosing the return bends.

5. An air heater as defined in claim 2 in which a skirt portion projects from the thick wall beyond each end face thereof and provides an enclosure around said return bends and at least one of said skirt portions has terminal post means extending outwardly therethrough and electrically connected to the helical coil.

6. An air heater as defined in claim 2 having a clamp within which the tubular body is peripherally confined and by which the heating unit is mounted on a support.

References Cited in the tile of this patent UNITED STATES PATENTS 1,057,745 Kohn Apr. 1, 1913 1,399,428 Hughes Dec. 6, 1921 1,419,309 Russell June 13, 1922 1,553,421 Woodson Sept. 15, 1925 1,756,033 Nordan Apr. 29, 1930 1,809,565 Ostrak June 9, 1931 2,611,790 Koch Sept. 23, 1952 2,744,946 Lewicki May 8, 1956 2,846,536 Drugmand et al. Aug. 5, 1958 FOREIGN PATENTS 246,364 Italy Mar. 22, 1926 545,875 France Aug. 3, 1922 

